[SOLVED] Setting PCIE slot to gen 3 instead of gen 4

[Iver Hicarte]

In the UEFI you can set the GPU's PCIE lane version on what version you want it, my question is if you set the lane to.....let's say version 3.0, will the lane of the NVME drives also change to that version? Correct me if I'm wrong and I am surely wrong, to my knowledge or how I understand NVME drives at least, is that these drives have specs saying GEN 3 AND GEN 4. So I'm assuming that the slots they attach to in the motherboard are like GPU slots.....which are PCIE slots. And if you change the GPU's PCIE lane version, do the drives' slots also change to that version? Or are the slots purely gen 3 and gen 4 already and you cannot change them?

 

[boju]

Good question, wouldn't mind the answer to that myself. Various search strings results mostly in comparisons, not really an answer on mixing pcie gens and how cpu would respond to that.

Pcie is backwards compatible, i know that. But would running pcie 3 and 4 together, gpu / nvme (vice versa), limit pcie generation across the board or is it independent? @InvalidError that's something you would know?

 

[InvalidError]

Pcie is backwards compatible, i know that. But would running pcie 3 and 4 together, gpu / nvme (vice versa), limit pcie generation across the board or is it independent? @InvalidError that's something you would know?

I would be inclined to believe that since every PCIe host can operate independently from all others with the default behavior of operating at the highest speed supported by both ends, the decision to make the PCIe speed limit apply to specific slots or have a per-slot setting is part of the PCIe host controller boot-time initialization (the BIOS is figuring out what is plugged in in which slot to setup bifurcation switches if applicable and setting the host's max speed to match the switches in case a CPU supporting higher speeds gets installed) and entirely at the motherboard manufacturer's discretion.

 

[Iver Hicarte]

Good question, wouldn't mind the answer to that myself. Various search strings results mostly in comparisons, not really an answer on mixing pcie gens and how cpu would respond to that.

Pcie is backwards compatible, i know that. But would running pcie 3 and 4 together, gpu / nvme (vice versa), limit pcie generation across the board or is it independent? @InvalidError that's something you would know?

We definitely need an answer on this one, this question just popped in my mind. Let's hope in the future we have a sure and solid answer instead of just relying on answers based on comparison.

 

[InvalidError]

We definitely need an answer on this one, this question just popped in my mind. Let's hope in the future we have a sure and solid answer instead of just relying on answers based on comparison.

Next time you reboot your computer, go in BIOS and see whether you have a global PCIe speed limit, a per-slot one or none at all depending on the motherboard manufacturer's needs and whims. In principle, the option is unnecessary since PCIe 4.0 devices that fail to establish a reliable connection should fall back to 3.0 or possibly lower if necessary. Manually forcing a lower speed is primarily for troubleshooting purposes when a device fails to reliably fall back on its own and causes problems.

 

[InvalidError]

BTW, just had to reboot to finish installing the Novermber Windows update. On my B560 TUF, the PCIe setup page has independent override controls for x16 and primary NVMe slots just as I suspected.

 

[boju]

Cool, so, on your board, if you were to run pcie 3 nvme from cpu the pcie slot would still run at 4?

 

[InvalidError]

Cool, so, on your board, if you were to run pcie 3 nvme from cpu the pcie slot would still run at 4?

Negotiating the highest speed possible on a per PCIe host controller basis is the expected behavior, every BIOS/board should be able to do this much unless there is a design flaw forcing a lower speed on one or more host controllers.

OP's question was about whether forcing a lower speed on the GPU slot would also lower the NVMe speed. The answer (at least for my board) is that PCIe limits are set independently. Mileage may vary between models and manufacturers.